My research interests mainly include quasars and active galactic nuclei (AGNs), supermassive black holes and their accretion physics. Recently we have discovered many new quasars at intemediate and high redshift using optical telescopes in China and the US, including LAMOST and MMT. With optical and near-infrared spectroscopy, we are carrying out detailed studies of the black hole masses and accretion rates of many quasars and AGNs.